CN204360391U - Fingerprint detection circuit and fingerprint sensor and finger print detection device - Google Patents

Abstract

The utility model discloses a fingerprint detection circuit, which comprises a signal generating unit, a transmitting electrode, a fingerprint detecting unit, a signal amplifier, an inductance element and a signal processing circuit, the signal generating unit is connected with the transmitting electrode, and the fingerprint detecting unit detects fingerprint ridge and valley information of a finger And output the electrical signal, the signal amplifier is connected with the fingerprint detection unit to amplify the electrical signal, the inductance element is connected between the negative input terminal and the output terminal of the signal amplifier, the signal processing circuit is connected to the output terminal of the signal amplifier and according to the amplified The electrical signal to calculate the finger capacitance. The above-mentioned fingerprint detection circuit uses an inductance element to realize the function that can only be realized by a large resistance, effectively reduces circuit noise while improving fingerprint detection accuracy, and significantly reduces power consumption and area of the circuit. The above-mentioned fingerprint detection circuit has a simple circuit and high stability, is easy to implement, and has low circuit cost. The utility model also discloses a fingerprint sensor and a fingerprint detection device.

Description

Fingerprint detection circuit, fingerprint sensor and fingerprint detection device

technical field

The utility model relates to the field of fingerprint identification, and more specifically relates to a fingerprint detection circuit, a fingerprint sensor and a fingerprint detection device.

Background technique

As people's requirements for information security are getting higher and higher, traditional digital passwords or Jiugongge passwords can no longer meet people's requirements for information security. Biometric identification is widely used in the new generation of electronic devices, and fingerprint is currently the most widely used biometric feature. The uneven shape of the surface of the fingerprint constitutes the lines of the fingerprint, and the lines are in the shape of ridges. The raised lines are called peaks, and the concave parts are called valleys. The fingerprint feature is a smooth texture pattern composed of peaks and valleys on the surface of the finger, which is highly random. Research shows that fingerprint features are unique and stable, and identity recognition can be realized accordingly.

Before performing fingerprint identification, it is first necessary to collect biological samples or fingerprint images and extract fingerprint features from them as a reference for fingerprint identification. The fingerprint features are stored in the fingerprint identification system; The fingerprint image is extracted from the fingerprint feature, and the fingerprint feature is compared with the previous fingerprint reference to achieve the purpose of identity verification.

Please refer to Fig. 1, Chinese patent 200710129193.0 discloses a fingerprint detection circuit, which includes an external electrode 10, a detection unit 20, a resistor 30 and a signal generation source 40, and the external electrode 10 and the signal generation source 40 are respectively coupled to the reference level Vcmb and Vcma, the detection unit 20 is coupled to the signal generating source 40 through the resistor 30, and the detection circuit further includes an output terminal OUT coupled between the detection unit 20 and the resistor 30, and the output terminal OUT is connected to the judgment circuit and the analog-to-digital converter. Different detection units 20 and different lines on the surface of the finger 50 equivalently form many capacitive components with different capacitance values. For the signal generating source 40, the resistor 30 and the capacitive component constitute a filter circuit, so the output terminal OUT According to the reference signal provided by the signal generating source 40, different detection signals are correspondingly generated according to the difference between the resistance value of the resistor 30 and the capacitance value of the capacitor component, thereby realizing fingerprint detection.

However, the above-mentioned technical solution has the following defects: firstly, because the capacitance of the capacitor component is very small, the resistor 30 is required to be very large in order to obtain an appropriate cut-off frequency, and it will consume a lot of cost to integrate it on the chip; secondly, when detecting a single fingerprint pixel It needs to go through multiple "comparator detection -> input signal adjustment" cycles to determine the final DC level. The higher the detection accuracy, the longer the detection cycle required, resulting in the incompatibility of the two important indicators of detection speed and detection accuracy. ; Finally, the signal generation source 40 of this patent and the analog-to-digital converter constitute a closed loop, which makes the circuit have the risk of loop instability.

To sum up, the existing fingerprint detection circuit has high circuit cost, poor circuit stability, and slow fingerprint detection speed.

Utility model content

The utility model aims at at least solving one of the technical problems existing in the prior art. Therefore, the utility model needs to provide a fingerprint detection circuit, a fingerprint sensor and a fingerprint detection device.

A fingerprint detection circuit. The fingerprint detection circuit realizes fingerprint detection by calculating finger capacitance. The fingerprint detection circuit includes a signal generation unit, a transmitting electrode, a fingerprint detection unit, a signal amplifier, an inductance element and a signal processing circuit. The signal generation unit and The transmitting electrode is connected to transmit an AC signal to the finger through the transmitting electrode, the fingerprint detection unit detects the fingerprint ridge and valley information of the finger and outputs an electrical signal, the signal amplifier is connected to the fingerprint detection unit and amplifies the electrical signal, The inductance element is connected between the negative input terminal and the output terminal of the signal amplifier, and the signal processing circuit is connected with the output terminal of the signal amplifier and calculates the finger capacitance according to the amplified electric signal.

The above-mentioned fingerprint detection circuit uses an inductance element to realize the function that can only be realized by a large resistance, and does not need a resistance element with a large resistance value, which effectively reduces the circuit noise while improving the fingerprint detection accuracy, and significantly reduces the power of the circuit. consumption and area. The above-mentioned fingerprint detection circuit has a simple circuit and high stability, is easy to implement, and has low circuit cost.

In one embodiment, the signal processing circuit calculates the finger capacitance C _f according to the following formula:

C _f =-Vo/Vi LS ² , where Vo is the voltage obtained by the signal processing circuit processing the amplified electrical signal, Vi is the voltage amplitude of the AC signal, L is the inductance of the inductive element, and S is the The frequency of the AC signal.

In one embodiment, the signal processing circuit includes an analog signal processing module, an analog-to-digital conversion module, and a digital signal processor connected in sequence, and the input end of the analog signal processing module is connected to the output end of the signal amplifier.

In one embodiment, the AC signal is a sine wave, a square wave or a triangle wave.

A fingerprint sensor includes a frame, a protective layer and a two-dimensional detection array formed by arranging multiple fingerprint detection units. The frame surrounds the two-dimensional detection array, and the protective layer covers the two-dimensional detection array.

A fingerprint detection device, including a fingerprint detection circuit and a fingerprint sensor, the fingerprint detection circuit realizes fingerprint detection by calculating finger capacitance, the fingerprint detection circuit includes a signal generating unit, a transmitting electrode, a signal amplifier, an inductance element and a signal processing circuit, the The fingerprint sensor includes a frame and a two-dimensional detection array composed of multiple fingerprint detection units arranged by arrangement. The frame surrounds the two-dimensional detection array. signal, the transmitting electrode is electrically connected to the frame, the two-dimensional detection array detects the fingerprint ridge and valley information of the finger and outputs an electrical signal, the signal amplifier is connected to the two-dimensional detection array and amplifies the electrical signal, the inductor The element is connected between the negative input terminal and the output terminal of the signal amplifier, and the signal processing circuit is connected with the output terminal of the signal amplifier and is used for calculating the finger capacitance according to the amplified electric signal.

In one embodiment, the signal processing circuit calculates the finger capacitance C _f according to the following formula:

C _f =-Vo/Vi LS ² , where Vo is the voltage obtained by the signal processing circuit processing the amplified electrical signal, Vi is the voltage amplitude of the AC signal, L is the inductance of the inductive element, and S is the The frequency of the AC signal.

In one embodiment, the signal processing circuit includes an analog signal processing module, an analog-to-digital conversion module, and a digital signal processor connected in sequence, and the input end of the analog signal processing module is connected to the output end of the signal amplifier.

In one embodiment, the AC signal is a sine wave, a square wave or a triangle wave.

In one embodiment, the fingerprint sensor further includes a protective layer covering the two-dimensional detection array.

The above-mentioned fingerprint detection device uses an inductance element to realize the function that can only be realized by a large resistance, and does not need a resistance element with a large resistance value, which effectively reduces the circuit noise while improving the fingerprint detection accuracy, and significantly reduces the power of the circuit. consumption and area. The circuit of the above-mentioned fingerprint detection device is simple and highly stable, easy to implement, and low in circuit cost.

Additional aspects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Description of drawings

The above and/or additional aspects and advantages of the present utility model will become apparent and easy to understand from the description of the embodiments in conjunction with the following drawings, wherein:

FIG. 1 is a schematic diagram of a fingerprint detection circuit in the prior art.

Fig. 2 is a schematic diagram of a fingerprint detection circuit in a preferred embodiment of the present invention.

Fig. 3 is a schematic structural diagram of a fingerprint sensor in a preferred embodiment of the present invention.

Fig. 4 is a schematic structural diagram of a fingerprint detection device in a preferred embodiment of the present invention.

Detailed ways

Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present utility model, but should not be construed as limiting the present utility model.

In the description of the present utility model, it should be understood that the terms "first" and "second" are only used for descriptive purposes, and cannot be interpreted as indicating or implying relative importance or implicitly specifying the quantity of indicated technical features . Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of said features. In the description of the present utility model, "plurality" means two or more, unless otherwise specifically defined.

In the description of the present utility model, it should be noted that, unless otherwise clearly stipulated and limited, the terms "installation", "connection", and "connection" should be understood in a broad sense, for example, it can be a fixed connection or a flexible connection. Detachable connection, or integral connection; it can be mechanical connection, electrical connection or mutual communication; it can be directly connected or indirectly connected through an intermediary, and it can be the internal communication of two components or the mutual communication of two components role relationship. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present utility model according to specific situations.

The disclosure below provides many different implementations or examples for realizing different structures of the present invention. In order to simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the utility model. Furthermore, the present invention may repeat reference numerals and/or reference letters in different instances, such repetition is for the purpose of simplicity and clarity, and does not in itself indicate a relationship between the various embodiments and/or arrangements discussed. In addition, various specific process and material examples are provided herein, but one of ordinary skill in the art may recognize the use of other processes and/or the use of other materials.

Please refer to FIG. 2 , the fingerprint detection circuit 100 of the preferred embodiment of the present invention includes a signal generating unit 102 , a transmitter electrode 104 , a fingerprint detection unit 106 , a signal amplifier 108 , an inductance element 110 and a signal processing circuit 112 . The fingerprint detection circuit 100 realizes fingerprint detection by calculating finger capacitance.

The signal generating unit 102 is connected to the transmitting electrode 104 and transmits an AC signal to the finger through the transmitting electrode 104 . For example, the AC signal is a sine wave, a square wave or a triangle wave. The voltage of the AC signal is Vi, and the frequency of the AC signal is S.

The fingerprint detection unit 106 detects the fingerprint ridge-valley information of the finger and outputs an electrical signal. The AC signal is transmitted to the finger through the transmitting electrode 104, and a capacitor C _f is formed between the finger and the fingerprint detection unit 106. The distance between them is relatively far, so the capacitance formed between the peak and the fingerprint detection unit 106 and the capacitance formed between the valley and the fingerprint detection unit 106 are different, as long as the capacitance C _f between them is detected, it can be Separate the ridge-valley features of the fingerprint information.

The signal amplifier 108 is connected with the fingerprint detection unit 106 and amplifies the electrical signal. Because the detected output voltage signal is very small, it needs to be connected to a signal amplifier 108 to amplify the obtained voltage signal.

The inductance element 110 is connected between the negative input end and the output end of the signal amplifier 108 , and the inductance element 110 is used for filtering. The positive input terminal of the signal amplifier 108 is grounded.

The signal processing circuit 112 is connected to the output terminal of the signal amplifier 108 and calculates finger capacitance according to the electrical signal. The finger capacitance here specifically refers to the capacitance C _f between the finger and the fingerprint detection unit 106 . In this embodiment, the signal processing circuit 112 includes an analog signal processing module (ASP processing module) 114, an analog-to-digital conversion module (A/D module) 116, and a digital signal processor (DSP) 118 connected in sequence. The input of the module 114 is connected to the output of the signal amplifier 108 .

Specifically, the signal processing circuit 112 calculates the finger capacitance C _f according to the following formula: C _f =-Vo/Vi LS ² , where Vo is the voltage obtained by the signal amplifier 108 processing the amplified electrical signal, and Vi is the AC The voltage amplitude of the signal, L is the inductance of the inductance element 110, and S is the frequency of the AC signal.

The above-mentioned fingerprint detection circuit 100, using an inductance element 110 can realize the function that can only be realized by a large resistance, and does not need a resistance element with a large resistance value, which effectively reduces the circuit noise while improving the fingerprint detection accuracy, and significantly reduces the circuit size. power consumption and area. The circuit of the fingerprint detection circuit 100 is simple and highly stable, easy to realize and low in circuit cost.

Please refer to FIG. 3 in conjunction with FIG. 4 , the fingerprint sensor 200 of the preferred embodiment of the present invention includes a frame 202 , a protective layer 204 (see FIG. 4 ) and a two-dimensional detection array 208 composed of a plurality of fingerprint detection units 206 arranged in arrangement.

The frame 202 surrounds the two-dimensional detection array 208 and provides a reference signal (such as an AC signal) through the finger during fingerprint detection.

The protection layer 204 covers the two-dimensional detection array 208 . Specifically, the top conductor layer 210 of the fingerprint detection unit 206 is covered with a protection layer 204 (refer to FIG. 4 ). The material of the protection layer 204 is an insulating material, which serves as a package structure of the fingerprint sensor 200 and provides protection for the internal detection structure.

The fingerprint detection unit 206 in Fig. 3 completes the acquisition of a single pixel of the fingerprint image, and the capacitance C _f formed between the top conductor layer 210 of the fingerprint detection unit 206 and the finger represents the peak or valley of the fingerprint. Therefore, the multiple capacitances C _f formed by all the detection units 206 of the detection array 208 and the finger represent the characteristics of the fingerprint image.

When the finger 500 is placed on the fingerprint sensor 200 , the frame 202 is connected with the finger. The frame 202 provides a reference signal through the finger 500 and completes the collection of the fingerprint pattern together with the detection array 208 .

The above-mentioned fingerprint sensor 200 can form a fingerprint detection device with the fingerprint detection circuit, and provide the required finger capacitance for the fingerprint detection circuit.

Please refer to Fig. 4 and in conjunction with Fig. 3, the fingerprint detection device 300 of the preferred embodiment of the present invention includes a fingerprint detection circuit 302 and a fingerprint sensor 200, and the fingerprint detection circuit 302 includes a signal generating unit 306, a transmitting electrode 308, a signal amplifier 310, An inductance element 312 and a signal processing circuit 314 . The fingerprint detection circuit 302 realizes fingerprint detection by calculating finger capacitance.

The signal generating unit 306 is connected to the transmitting electrode 308 and transmits an AC signal to the finger through the transmitting electrode 308 . For example, the AC signal is a sine wave, a square wave or a triangle wave. The voltage of the AC signal is Vi, and the frequency of the AC signal is S.

The signal amplifier 310 is connected with the fingerprint sensor 200 and amplifies the electrical signal output by the fingerprint sensor 200 . Because the detected output voltage signal is very small, it needs to be connected to a signal amplifier 310 to amplify the obtained voltage signal.

The inductance element 312 is connected between the negative input end and the output end of the signal amplifier 310, and the inductance element 312 performs filtering. The positive input terminal of the signal amplifier 310 is grounded. The signal amplifier 310 is an operational amplifier. The signal processing circuit 314 is connected to the output terminal of the signal amplifier 310 and calculates finger capacitance according to the electrical signal. In this embodiment, the signal processing circuit 314 includes an analog signal processing module (ASP processing module) 316, an analog-to-digital conversion module (A/D module) 318, and a digital signal processor (DSP) 320 connected in sequence. The input terminal of the module 316 is connected to the output terminal of the signal amplifier 310 .

The frame 202 of the fingerprint sensor 200 is electrically connected to the transmitting electrode 308, and provides a reference signal (such as an AC signal) through the finger during fingerprint detection.

When detecting finger fingerprints, the signal generating unit 306 transmits an AC signal to the finger through the emitter electrode 308 and the frame 202. For each fingerprint detection unit 206, its conductor layer 210 is used as a detection electrode that forms a fingerprint sensing capacitance with the surface of the finger. Therefore, the fingerprint The detection unit 206 can be regarded as a detection electrode, and the positive input terminal of the signal amplifier 310 is connected to a fixed potential 0, so that the detection electrode 206 can always be kept at a fixed potential 0 through the imaginary short characteristic of the positive and negative input ports of the signal amplifier 310 .

As shown in Figure 4, when the finger 500 is placed on the protective layer 204, the fingerprint on the upper surface of the protective layer 204 and the detection electrode 206 below the protective layer 204 form an inductive capacitance C _f , due to the structure of the fingerprint, the peak The size of the inductive capacitance C _f formed by the valley and the detection electrode is different, and the fingerprint image information on the finger surface can be obtained by detecting C _f .

The analog signal output by the signal amplifier 310 needs to be processed by the ASP processing module 316 for integer and integral processing, the A/D module 318 for analog-to-digital conversion, and the digital result of Vo can only be obtained after being processed by the DSP320. According to Vo=-Vi LC _f S ² , then C _f =-Vo/Vi LS ² , the size of finger capacitance C _f can be obtained.

The above-mentioned fingerprint detection device 300 uses an inductance element 312 to realize the function that can only be realized by a large resistance, and does not need a resistance element with a large resistance value, which effectively reduces the circuit noise while improving the fingerprint detection accuracy, and significantly reduces the circuit size. power consumption and area. The circuit of the above-mentioned fingerprint detection device 300 is simple and highly stable, easy to implement, and low in circuit cost.

In the description of this specification, reference to the terms "one embodiment", "some embodiments", "exemplary embodiments", "example", "specific examples", or "some examples" etc. The specific features, structures, materials or features described in the embodiments or examples are included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the described specific features, structures, materials or characteristics may be combined in any suitable manner in any one or more embodiments or examples.

Although the embodiments of the present invention have been shown and described, those skilled in the art can understand that various changes, modifications, substitutions and modifications, the scope of the present invention is defined by the claims and their equivalents.

Claims (10)

1. A fingerprint detection circuit, this fingerprint detection circuit realizes fingerprint detection by calculating finger capacitance, it is characterized in that, this fingerprint detection circuit comprises signal generating unit, transmitting electrode, fingerprint detection unit, signal amplifier, inductive element and signal processing circuit , the signal generating unit is connected with the emitting electrode and transmits an AC signal to the finger through the emitting electrode, the fingerprint detection unit detects the fingerprint ridge and valley information of the finger and outputs an electrical signal, the signal amplifier is connected with the fingerprint detection unit and The electrical signal is amplified, the inductance element is connected between the negative input terminal and the output terminal of the signal amplifier, the signal processing circuit is connected to the output terminal of the signal amplifier and calculates the finger capacitance according to the amplified electrical signal. 2. The fingerprint detection circuit according to claim 1, wherein the signal processing circuit calculates the finger capacitance C _f according to the following formula: C _f =-Vo/Vi LS ² , wherein Vo is the signal processing circuit processing the The voltage obtained from the amplified electrical signal, Vi is the voltage amplitude of the AC signal, L is the inductance of the inductance element, and S is the frequency of the AC signal. 3. The fingerprint detection circuit as claimed in claim 1, wherein the signal processing circuit comprises an analog signal processing module, an analog-to-digital conversion module and a digital signal processor connected in sequence, and the input end of the analog signal processing module is connected to the output of the signal amplifier. 4. The fingerprint detection circuit according to claim 1, wherein the AC signal is a sine wave, a square wave or a triangle wave. 5. A fingerprint sensor, characterized in that it comprises a frame, a protective layer and a two-dimensional detection array formed by arranging a plurality of fingerprint detection units, the frame surrounds the two-dimensional detection array, and the protective layer covers the two-dimensional detection array. dimensional detection array. 6. A fingerprint detection device, characterized in that it comprises a fingerprint detection circuit and a fingerprint sensor, the fingerprint detection circuit realizes fingerprint detection by calculating finger capacitance, and the fingerprint detection circuit includes a signal generating unit, a transmitting electrode, a signal amplifier, an inductive element and a signal processing circuit, the fingerprint sensor includes a frame and a two-dimensional detection array formed by arranging multiple fingerprint detection units, the frame surrounds the two-dimensional detection array, the signal generating unit is connected to the emitting electrode and passed through The transmitting electrode transmits an AC signal to the finger, the transmitting electrode is electrically connected to the frame, the two-dimensional detection array detects the fingerprint ridge-valley information of the finger and outputs an electrical signal, the signal amplifier is connected to the two-dimensional detection array and transmits the electrical signal For amplification processing, the inductance element is connected between the negative input terminal and the output terminal of the signal amplifier, and the signal processing circuit is connected to the output terminal of the signal amplifier and calculates the finger capacitance according to the amplified electrical signal. 7. The fingerprint detection device according to claim 6, wherein the signal processing circuit calculates the finger capacitance C _f according to the following formula: C _f =-Vo/Vi LS ² , where Vo is the signal processing circuit processing the The voltage obtained from the amplified electrical signal, Vi is the voltage amplitude of the AC signal, L is the inductance of the inductance element, and S is the frequency of the AC signal. 8. The fingerprint detection device according to claim 6, wherein the signal processing circuit comprises an analog signal processing module, an analog-to-digital conversion module and a digital signal processor connected in sequence, and the input end of the analog signal processing module is connected to the output of the signal amplifier. 9. The fingerprint detection device according to claim 6, wherein the AC signal is a sine wave, a square wave or a triangle wave. 10. The fingerprint detection device according to claim 6, wherein the fingerprint sensor further comprises a protection layer covering the two-dimensional detection array.